Solventless adhesive composition

Abstract

The invention relates to an adhesive composition comprising at least: - a compound comprising at least two epoxy functions; - a polyphenolic compound chosen from trigalloyl glucoses, pentagalloyl glucoses, decagalloyl glucoses and mixtures of same; - a compound comprising at least one double bond that can have a linear, branched and / or crosslinked macrostructure which can be organised into a structure of the "core shell rubber", micelle or particle type; and which comprises less than 0.1 wt.-% catalyst, with the catalyst not comprising an antimony-based catalyst.

Description

[0001] Solvent-free adhesive composition

[0002]

[0001] The field of the present invention is that of adhesive compositions or "glues" intended to make metallic reinforcing elements adhere to rubber matrices such as those commonly used in semi-finished rubber articles or products.

[0003]

[0002] The present invention relates more particularly to an adhesive composition based on a compound comprising at least two epoxy functions, a polyphenolic compound comprising one or more aromatic ring(s), and a compound comprising at least one double bond which may have a linear, branched and / or cross-linked macrostructure which may organize itself into a "core shell rubber" type structure or micelle or particle.

[0004]

[0003] Prior art is known of steel reinforcement elements coated with aqueous adhesive layers based on a phenol-aldehyde resin and an unsaturated elastomer latex, in particular coated steel reinforcement elements capable of reinforcing tire structures, in particular of application EP 3102407.

[0005]

[0004] Prior art is also known from document EP 3688110 of metallic reinforcement elements covered with an adhesive composition based on at least one phosphate salt and a resin based on a compound comprising at least one aldehyde function and a phenol and in particular to coated steel reinforcement elements capable of reinforcing tire structures.

[0006]

[0005] The problem with aqueous metal-rubber adhesive compositions is that they are most often sensitive to water and it is interesting to improve their protective action against aging mechanisms under humid atmosphere with thermal.

[0007]

[0006] Adhesive compositions comprising epoxy resins, "core shell rubber" particles, a phenolic compound having 2 hydroxyl functions, a catalyst to promote the reaction between this compound and the epoxy, and a crosslinking agent are also known from the prior art and in particular from JP 2020152775.

[0008]

[0007] The problem with this adhesive composition is that it requires the addition of a catalyst. The use of a catalyst constrains the process of obtaining the composition, particularly the mixing step, which must be carried out at a temperature lower than the curing temperature. Adding a catalyst also increases the cost of the adhesive composition. Furthermore, the catalyst also affects the glass transition temperature of the epoxy resin formed, which limits the range of applications for the product containing the composition. Moreover, some of these catalysts, used in compositions to reduce curing time and temperature, present risks to the environment or human health. This is particularly true of triphenylphosphine.

[0009]

[0008] However, during their research, the Applicant discovered an adhesive composition that meets the above objective without adding a catalyst, while ensuring good adhesion to a metallic reinforcement element and providing effective protection against thermal aging mechanisms under a humid atmosphere.

[0010]

[0009] The invention aims to find an adhesive composition to overcome these drawbacks.

[0011]

[0010] To this end, the invention relates to an adhesive composition comprising at least:

[0012] - a compound comprising at least two epoxy functions;

[0013] - a polyphenolic compound selected from trigalloyl glucoses, pentagalloyl glucoses, decagalloyl glucoses and mixtures thereof;

[0014] - a compound comprising at least one double bond which may have a linear, branched and / or cross-linked macrostructure which may organize itself into a "core shell rubber" type structure or micelle or particle; and the composition comprising less than 0.1% by weight of catalyst with the catalyst not comprising an antimony-based catalyst.

[0015]

[0011] This multi-component formulation offers an excellent compromise in terms of the mechanical strength of the assembly after fabrication and over time. The epoxy resin formed provides good adhesion to metal, for example, and also protects it from aging, particularly thermal and humid conditions. It also contains little or no catalyst to avoid all the processing and storage drawbacks described above.

[0016]

[0012] By "core shell rubber" is meant a block elastomer that can organize itself into a core-crown structure.

[0017]

[0013] Here the hardener, the polyphenolic compound, ensures the crosslinking of the epoxy resin.

[0018]

[0014] By definition, the catalyst accelerates the polyaddition reaction of the epoxy compound and the polyphenolic compound. Examples of suitable catalysts include triphenylphosphine, imidazole and its derivatives, and certain tertiary amines such as triethanolamine, triethylamine, or n-butylamine.

[0015] Preferably, the catalyst is selected from triphenylphosphine, imidazole and its derivatives, and certain tertiary amines such as triethanolamine, triethylamine, or n-butylamine.

[0019]

[0016] Preferably, the catalyst does not include antimony-based catalysts or any other compound requiring precautions due to their harmfulness. The use of antimony-based catalysts is to be limited as much as possible, or even eliminated.

[0020]

[0017] The expression "composition based on" should of course be understood as a composition comprising the mixture and / or reaction products of the various basic constituents used for this composition, some of which may be intended to react or are likely to react with each other or with their immediate chemical environment, at least in part, during the various manufacturing phases of the composition, the reinforcing element, the composites, or the finished articles, in particular during a curing step.

[0018] Any range of values ​​designated by the expression "between a and b" represents the range of values ​​from greater than a to less than b (i.e., excluding the limits a and b), while any range of values ​​designated by the expression "from a to b" means the range of values ​​from a to b (i.e., including the strict limits a and b).

[0021]

[0019] Within the scope of the invention, the carbon products mentioned in the description may be of fossil origin or bio-based. In the latter case, they may be, partially or totally, derived from biomass or obtained from renewable raw materials derived from biomass.

[0022]

[0020] Within the scope of the invention, it may also be envisaged that the carbon products mentioned in the description include isotopes of certain chemical elements.

[0023]

[0021] Advantageously, the adhesive composition comprises less than 5% by weight of water, preferably less than 1% by weight of water and more preferably is free of water.

[0024]

[0022] Advantageously, the adhesive composition comprises less than 5% by weight of organic solvent, preferably less than 1% by weight of organic solvent and more preferably is free of organic solvent.

[0025]

[0023] This "epoxy-phenolic hardener-double bond compound" adhesive composition is formulated without organic solvents, while remaining liquid to facilitate its application to the reinforcement. This significantly reduces the environmental impact and industrial production cost of the adhesive composition. No energy is required to evaporate the organic solvent. There are no VOC (volatile organic compound) emissions during the application or heat treatment of the adhesive composition.

[0026]

[0024] By definition, an organic solvent is understood to be a compound that must be evaporated at least once during the manufacturing of the adhesive composition. Thus, the organic solvent allows the reactants to dissolve and to come into contact with the other reactants. The organic solvent does not react chemically with the dissolved compounds; it is inert.

[0027]

[0025] Advantageously, the adhesive composition comprises less than 0.01% by weight of catalyst and more preferably is free of catalyst.

[0028]

[0026] Preferably, the composition is catalyst-free. This makes the adhesive composition easier to use and allows it to be stored in a batch process. Another advantage is its relatively low cost.

[0029]

[0027] The adhesive composition therefore comprises at least one (i.e. one or more) "epoxy-phenolic hardener-compound comprising a double bond" resin based on at least one (i.e. one or more) compound comprising at least one epoxy function, at least one (i.e. one or more) polyphenolic compound and at least one (i.e. one or more) compound comprising at least one double bond having a "core shell rubber" type structure or micelle or particle, constituents which will be described in detail below.

[0030]

[0028] 1.1 - Compound comprising at least two epoxy functions

[0029] The first constituent of the adhesive composition is a compound comprising at least two epoxy functions.

[0031]

[0030] Preferably, the compound comprising at least two epoxy groups is selected from 3,4-epoxycyclohexylmethyl 3,4-epoxycyclohexanecarboxylate, bis(3,4-epoxycyclohexylmethyl) adipate, and diglycidyl 1,2-cyclohexanedicarboxylate.

[0031] Preferably, the adhesive composition comprises at least two compounds comprising at least two epoxy groups; preferably, the second compound is selected from diglycidyl ether, poly(propylene glycol) diglycidyl ether, and 1,4-butanediol diglycidyl ether.

[0032]

[0032] I.2 - Polyphenolic compound

[0033]

[0033] The second constituent of the adhesive composition is a polyphenolic compound.

[0034]

[0034] Preferably, the polyphenolic compound is chosen from the tannin family and even more preferentially from the gallotannins.

[0035]

[0035] Preferably, the polyphenolic compound is chosen from 1,2,6-trigalloyl glucose, 1,3,6-trigalloyl glucose, 1,2,3,4,6-pentagalloyl glucose, tannic acid and mixtures thereof.

[0036]

[0036] I.3 - Compound comprising at least one double bond which may have a linear structure, a branched structure having a "core shell rubber" type structure or a micelle or particle

[0037]

[0037] The third constituent of the adhesive composition is a compound comprising at least one double bond which may have a linear, branched and / or cross-linked macrostructure which may organize itself into a “core shell rubber” type structure or micelle or particle.

[0038]

[0038] Preferably, the compound comprising at least one double bond which may have a linear, branched and / or cross-linked macrostructure which may organize itself into a "core shell rubber" type structure or micelle or particle is chosen from dicarboxy-terminated poly(acrylonitrile-co-butadiene), polybutadiene, polyisoprene, farnesene-butadiene copolymers and polybutadiene core shell rubber which may already be dispersed in the compound comprising at least two epoxy functions and mixtures of these compounds.

[0039]

[0039] Preferably, the "core shell rubber" are block elastomers, containing polybutadiene blocks and which are in the form of core-crown particles ("shell" in English) and previously dispersed in the compound having at least two epoxy functions such as for example the MX553 compound from Kaneka.

[0040]

[0040] I.4 - Manufacture of the adhesive composition

[0041]

[0041] The constituents of the adhesive composition are mixed at a temperature well chosen by a person skilled in the art in relation to the physical properties of the raw materials, for example 100°C, until a homogeneous mixture is obtained.

[0042] The use of a catalyst can, from this stage, be restrictive for the process of implementing the composition by limiting the mixing temperature in relation to the temperature range compatible with the catalyst.

[0043] The mixture can be used directly or stored before use and heated to adjust the viscosity according to the chosen coating method on the metal reinforcement element. The use of a catalyst can also be problematic for storing the mixture, which is restrictive and problematic for non-continuous application processes.

[0042]

[0044] In the final adhesive composition thus prepared, the hardener content, i.e. polyphenolic compound, ranges from 5 to 50% by weight, preferably from 10 to 30% by weight.

[0043]

[0045] Composite

[0044]

[0046] Another object of the invention relates to a rubber composite reinforced with at least one metallic reinforcing element covered with an adhesive composition as described above comprising a rubber matrix in which the covered metallic reinforcing element is embedded.

[0045]

[0047] Preferably, the metal reinforcement element is wire.

[0046]

[0048] Wire reinforcement elements are defined as long, elongated elements relative to their cross-section, regardless of the cross-section's shape (e.g., circular, oblong, rectangular, square, or even flat). These wire elements can be straight or non-straight, such as twisted or corrugated. When circular, the diameter of each wire reinforcement element is preferably less than 5 mm, and more preferably within the range of 0.1 to 0.5 mm. Also included are strips or bands with a significant length relative to their thickness.

[0047]

[0049] Preferably, the covered metal reinforcement element comprises one or more wire reinforcement elements, each with a steel core. The steel core is monolithic, meaning that it is, for example, formed from a single material or cast.

[0048]

[0050] Steel can exhibit a pearlitic, ferritic, austenitic, bainitic, martensitic microstructure or a microstructure resulting from a mixture of these microstructures.

[0049]

[0051] Preferably, the steel comprises a carbon content of 0.2% to 1% by mass, and more preferably 0.5% to 0.95% by mass. Preferably, the steel comprises a manganese content of 0.3% to 0.8% by mass, a silicon content of 0.1% to 0.6% by mass, a phosphorus content of not more than 0.05% included terminal by mass, a sulfur content of not more than 0.05% included terminal by mass, and a nitrogen content of not more than 0.008% included terminal by mass. Optionally, the steel comprises not more than 0.1% included terminal, preferably 0.05% included terminal, and more preferably 0.02% included terminal by mass of vanadium and / or molybdenum.

[0050]

[0052] In one embodiment, the steel used comprises less than 0.5%, preferably at most 0.05% inclusive of terminal, and more preferably at most 0.02% inclusive of terminal, by mass of chromium.

[0051]

[0053] In another embodiment using so-called stainless steel, the steel comprises at least 0.5% inclusive terminal, preferably at least 5% inclusive terminal and more preferably at least 15% inclusive terminal by mass of chromium.

[0054] Preferably, the steel comprises at least 2% inclusive of the terminal, preferably at least 4% inclusive of the terminal and more preferably at least 10% by mass of nickel.

[0052]

[0055] Advantageously, the steel core is devoid of a metallic coating layer.

[0053]

[0056] Preferably, the steel core of each of the one or more wire reinforcement elements is devoid of a metallic coating layer.

[0054]

[0057] By "without a metallic layer," we mean that the steel is not coated with a different metal. In particular, the reinforcing element is free of a layer of zinc, copper, tin, or an alloy of these metals, such as brass and bronze.

[0055]

[0058] Thus, in the embodiment where the coated steel reinforcement element comprises a single wire reinforcement element, the adhesive layer may cover some parts of this element or its entirety. In the embodiment where the coated steel reinforcement element comprises several wire reinforcement elements, the adhesive layer may cover several wire elements without covering others, or it may cover only certain parts of some or all of the wire elements.

[0056]

[0059] Advantageously, the adhesive composition directly covers a layer of metallic coating directly covering at least part of the steel core of the wire reinforcement element(s).

[0057]

[0060] Preferably, the metal of the metallic coating layer directly covering at least part of the steel core of the wire reinforcement element(s) is chosen from zinc, tin, copper and alloys of these metals.

[0061] Brass is an example of an alloy of these metals.

[0058]

[0062] First, the adhesive composition is coated onto the metal reinforcement from a coating line at a predetermined temperature range below the composition's initial curing temperature, while being adapted to the chosen process. Curing then takes place at a temperature range of 100 to 250°C, as determined by a person skilled in the art. The use of a catalyst in the composition necessitates handling it within a lower temperature range, which reduces the achievable viscosity range and can be limiting for the coating step.

[0059]

[0063] Obtaining the composite requires a further step in which the metallic reinforcing element is trapped in the elastomeric composition to achieve adhesion with the elastomeric matrix during the curing of the composite.

[0064] A particularly preferred process for coating the adhesive composition is that described in application FR2213647.

[0060]

[0065] A person skilled in the art will be able to adjust, where necessary, the temperature and duration of the above heat treatment, according to the specific conditions under which the invention is implemented, in particular the exact nature of the adhesive composition or the type of steel. In particular, a person skilled in the art will benefit from performing temperature and treatment duration sweeps in order to determine, through successive approximations, the operating conditions leading to the best adhesion results for each specific embodiment of the invention.

[0061]

[0066] The invention therefore applies to any type of rubber composite that can be obtained by the process described above, comprising at least one rubber matrix, in particular diene elastomer, linked to the metallic reinforcement element via an adhesive interface based on the adhesive composition described above.

[0062]

[0067] Such composites include pipes, seals, belts, conveyor belts, tracks, and vehicle tires, both in their raw state (i.e., before cross-linking or vulcanization) and in their cured state (after cross-linking or vulcanization). In preferred forms, such composites take the shape of a sheet or strips.

[0063]

[0068] The diene elastomer of the composite is preferably chosen from the group consisting of polybutadienes (BR), natural rubber (NR), synthetic polyisoprenes (IR), butadiene-styrene copolymers (SBR), isoprene-butadiene copolymers (BIR), isoprene-styrene copolymers (SIR), butadiene-styrene-isoprene copolymers (SBIR), and mixtures of these elastomers. Other examples include a copolymer of ethylene and a 1,3-diene, a copolymer of ethylene and 1,3-butadiene, and an ethylene-butadiene elastomer, designated as "EBR". A preferred embodiment consists of using an "isoprene" elastomer, that is to say a homopolymer or a copolymer of isoprene, in other words a diene elastomer chosen from the group consisting of natural rubber (NR), synthetic polyisoprenes (IR), the various isoprene copolymers and mixtures of these elastomers.Among butadiene copolymers, butadiene-styrene (SBR), isoprene-butadiene (BIR), and isoprene-butadiene-styrene (SBIR) copolymers are particularly noteworthy. This butadiene elastomer is preferably a cis-1,4 polybutadiene. The isoprene elastomer is preferably natural rubber or a synthetic cis-1,4 polyisoprene.

[0064]

[0069] PNEUMATIC

[0065]

[0070] Another object of the invention relates to a tire comprising at least one rubber composite as described above.

[0066]

[0071] The composite is advantageously usable for reinforcing tires of all types of vehicles, in particular passenger vehicles or industrial vehicles such as heavy goods vehicles.

[0067]

[0072] As an example, the attached figure 1 represents in a very schematic way (without respecting a specific scale), a radial section of a tire according to the invention for a heavy goods vehicle.

[0068]

[0073] This tire 1 has a crown 2 reinforced by a crown reinforcement or belt 6, two sidewalls 3, and two bead 4, each bead 4 being reinforced with a strand 5. The crown 2 is surmounted by a tread not shown in this schematic figure. A carcass reinforcement 7 is wound around the two strands 5 in each bead 4, the folded edge 8 of this reinforcement 7 being, for example, oriented towards the outside of the tire 1, which is shown here mounted on its rim 9.The carcass reinforcement 7 is known per se to consist of at least one layer reinforced by so-called "radial" cables, for example metallic, that is to say that these cables are arranged practically parallel to each other and extend from one bead to the other so as to form an angle between 80° and 90° with the median circumferential plane (plane perpendicular to the axis of rotation of the tire which is located halfway between the two beads 4 and passes through the middle of the apex reinforcement 6).

[0074] This tire 1 of the invention has, for example, the characteristic that at least one apex reinforcement 6 and / or its carcass reinforcement 7 comprises a reinforcing element in coated steel or a composite according to the invention.

[0069]

[0075] Of course, the invention relates to the objects previously described, namely the coated steel reinforcement element and the rubber composite as pneumatically comprising it, both in the raw state (before baking or vulcanization) and in the baked state (after baking).

[0070]

[0076] EXAMPLES OF INVENTION IMPLEMENTATION AND COMPARATIVE TESTS

[0071]

[0077] These tests demonstrate that:

[0072] - adhesion to a rubber matrix of metallic reinforcement elements covered by the adhesive composition according to the invention is acceptable;

[0073] - the adhesive composition allows for long-lasting adhesion of the reinforcing elements and enables resistance to thermal aging under humid atmosphere.

[0074]

[0078] To this end, several adhesive compositions, hereinafter referred to as C-1, C-2 and T-0 to T-2, were prepared as described above. Their formulations (expressed as mass percentages) are presented in the attached Table 1.

[0079] Each adhesive composition C-1 and C-2 is based on an adhesive composition according to the invention.

[0075]

[0080] Composition T-0 represents the brass-plated reinforcing element not covered by a composition.

[0076]

[0081] Composition T-1, covered by application EP3688110, is an aqueous composition based on phloroglucinol, terephthalaldehyde, sodium phosphate, elastomeric latex, and ammonia. This composition is outside the scope of the invention.

[0077]

[0082] Composition T-2 is a control composition also outside the scope of the invention.

[0078]

[0083] We tested here metallic reinforcement elements forming a 1+6+12 type assembly with the central wire having a diameter of 0.20 mm and the other wires 0.18 mm (19.18 cables). These are commonly used for making carcass plies for heavy-duty tires. The individual wires of the metallic reinforcement elements are steel wires coated with a layer of brass. The brass thickness ranges from 50 nm to 300 nm.

[0079]

[0084] The rubber matrix composition is a conventional composition suitable for calendering metallic tire plies, based on natural rubber, carbon black, and common additives. In this case, the rubber composition comprises 100 parts per million (ppm) of natural rubber, 47 parts per million (ppm) of 300 series carbon black, 1.5 parts per million (ppm) of N-1,3-dimethylbutyl-N-phenyl-para-phenylenediamine, 1.1 parts per million (ppm) of a cobalt salt, 0.9 parts per million (ppm) of stearic acid, 4.5 parts per million (ppm) of insoluble molecular sulfur, 0.8 parts per million (ppm) of N,N-dicyclohexyl-2-benzothiazolesulfamide, 0.15 parts per million (ppm) of a retarder, and 7.5 parts per million (ppm) of ZnO.

[0080]

[0085] The reinforcements are coated with adhesive compositions and then undergo a heat treatment for curing for 2 minutes at 220°C (for example). The coated reinforcements and rubber compositions are used to fabricate a reinforced product in the form of a test specimen according to the following protocol:

[0081] A rubber block is made from two plates, applied one on top of the other before curing. Both plates of the block are made of the same rubber compound. During the block's construction, the metal reinforcing elements are sandwiched between the two plates in their raw state, at equal intervals, with one end of the reinforcing element protruding on either side of the plates, long enough to allow for subsequent tensile strength. The block, including the reinforcements, is then cured. As an example, in this case, the block is cured at 140°C for a time ranging from 5 to 50 minutes, depending on the composition, under a pressure of 6 tons.

[0082]

[0086] After curing, the composite specimen, consisting of the cross-linked block and coated metal reinforcement elements, is placed in the jaws of a suitable tensile testing machine. This allows each section to be tested individually at a specific speed and temperature (for example, in this case, 100 mm / min at ambient temperature). Adhesion levels are characterized by measuring the pull-out force required to detach the sections from the specimen. The initial pull-out test at 20°C is shown in Table 1 below. The pull-out force result represented by 100 is the initial pull-out level measured on the control T-0; a value below 60 is unacceptable.

[0083]

[0087] Table 1 below shows the evolution of the pull-off force, taking as a base of 100 the brass-plated control not coated with an adhesive composition T-0

[0084]

[0088] [Table 1]

[0085] (1) Phloroglucinol (from Chem Pacific; 99% purity);

[0086] (2) Tannic acid (CAS No. 1401-55-4 of Sigma-Aldrich);

[0087] (3) Neopentylglycol diglycidyl ether (from Sigma Aldrich); (4) MX553: 3,4-Epoxycyclohexylmethyl 3,4-epoxycyclohexanecarboxylate containing 30% by mass of "core shell rubber" (from Kaneka);

[0088] (5) 3,4-Epoxycyclohexylmethyl 3,4-epoxycyclohexanecarboxylate (from Sigma Aldrich);

[0089] (6) 1,4-benzenedicarboxaldehyde (from Sigma-Aldrich).

[0089] Thus, it can be seen that composition C-1 according to the invention has an acceptable initial adhesion level, at the same level as control T-1. And composition C-2 has a significantly improved initial adhesion level compared to control T0 and control T1.

[0090]

[0090] The T-2 control without polyphenolic compound according to the invention has a level of adhesion below that of the T-0 control.

[0091]

[0091] Table 2 below represents the evolution of the pull-out force, taking the initial force level as a base of 100 for each composition, and we look at the evolution over time of the pull-out force of each reinforcement element in thermal aging under a humid atmosphere, 95% relative humidity (RH) and 55°C.

[0092]

[0092] These measurements are carried out initially and then at 7 days and 14 days after aging at 55°C under 95% relative humidity.

[0093]

[0093] [Table 2]

[0094]

[0094] Compared to the uncoated brass RO witness and the reinforcement covered by the aqueous adhesive composition T-1, the reinforcements covered with compositions C-1 and C-2 according to the invention do indeed show a durability of the adhesion of the reinforcement element in humid aging: 95% RH and 55°C.

[0095]

[0095] Thus the compositions according to the invention make it possible to constitute effective protection against the thermal aging mechanisms under a humid atmosphere of the metallic reinforcement elements.

[0096]

[0096] As another advantage related to the invention, it will be noted that the adhesive composition is usable and effective on steel reinforcement elements comprising wire reinforcement elements without metallic coating and more preferably without metallic coating chosen from zinc, copper, tin and alloys of these metals, for example brass.

[0097]

[0097] The invention is not limited to the embodiments described above.

Claims

Demands 1. Adhesive composition characterized in that the adhesive composition comprises at least: - a compound comprising at least two epoxy functions; - a polyphenolic compound selected from trigalloyl glucoses, pentagalloyl glucoses, decagalloyl glucoses and mixtures thereof; - a compound comprising at least one double bond which may have a linear, branched and / or cross-linked macrostructure which may organize itself into a "core shell rubber" type structure or micelle or particle; and the composition comprising less than 0.1% by weight of catalyst with the catalyst not comprising an antimony-based catalyst.

2. Adhesive composition according to the preceding claim, comprising less than 5% by weight of water, preferably less than 1% by weight of water and more preferably is free of water.

3. Adhesive composition according to any one of the preceding claims, wherein the adhesive composition comprises less than 5% by weight of organic solvent, preferably less than 1% by weight of organic solvent and more preferably is free of organic solvent.

4. Adhesive composition according to any one of the preceding claims, wherein the catalyst is selected from triphenylphosphine, imidazole and its derivatives, certain tertiary amines such as triethanolamine, triethylamine or n-butylamine.

5. Adhesive composition according to any one of the preceding claims, wherein the adhesive composition comprises less than 0.01% by weight of catalyst and more preferably is free of catalyst.

6. Adhesive composition according to any one of the preceding claims, wherein the compound comprising at least two epoxy functions is selected from 3,4-epoxycyclohexylmethyl 3,4-epoxycyclohexanecarboxylate, bis(3,4-epoxycyclohexylmethyl) adipate and diglycidyl 1,2-cyclohexanedicarboxylate.

7. Adhesive composition according to the preceding claim, wherein the adhesive composition comprises at least two compounds having at least two epoxy functions, preferably the second compound is selected from diglycidyl ether, poly(propylene glycol) diglycidyl ether and 1,4-butanediol diglycidyl ether.

8. Adhesive composition according to any one of the preceding claims, wherein the polyphenolic compound is selected from the 1,2,6-trigalloyl glucose, 1,3,6-trigalloyl glucose, 1,2,3,4,6-pentagalloyl glucose, tannic acid and mixtures thereof.

9. Adhesive composition according to any one of the preceding claims, wherein the compound comprising at least one double bond which may have a linear, branched and / or crosslinked macrostructure which may organize itself into a "core shell rubber" type structure or micelle or particle is selected from dicarboxy-terminated poly(acrylonitrile-co-butadiene), polybutadienes, polyisoprenes, farnesene-butadiene copolymers and polybutadiene core shell rubber which may already be dispersed in the compound comprising at least two epoxy functions and mixtures of these compounds.

10. Adhesive composition according to any one of the preceding claims, wherein the content of polyphenolic compound ranges from 5 to 50% by weight, preferably from 10 to 30% by weight.

11. Rubber composite reinforced with at least one steel reinforcing element covered with an adhesive composition according to any one of claims 1 to 10 comprising a rubber matrix in which the covered steel reinforcing element is embedded.

12. Tire comprising at least one rubber composite according to claim 11.

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